The invention relates in general to energy conservation by controlling the delivery of a fraction of positive or negative energy from an AC source of power to a DC device, such as a DC motor. More specifically and with reference to the embodiment described herein, the invention relates to controlling the speed and direction of an AC powered DC motor in linear relationship to the magnitude and polarity of a DC reference signal.
It has been known in the prior art to control both speed and direction of a DC motor. Such prior art includes the use of a triggerable bidirectional current conducting device, such as a triac, connected in series with a DC motor across an AC source. The motor direction is controlled by triggering the triac into conduction during either the positive or negative half cycle of the AC source. One such example in the prior art takes the form of the U.S. Pat. No. 3,857,077 to T. E. Kasmer. While Kasmer provides directional control there is no means provided for linearly controlling the operation in relation to a command signal, such as a DC reference. Control is only achieved during a portion of each of the half cycles and, hence, this limits the amount of energy that may be delivered to the DC motor.